Axial bearing wear detection device for canned motor

ABSTRACT

An axial position detection circuit detects the axial position of a rotor from the difference in voltages generated at axial position detection coils disposed at both ends in the axial direction of a stator of a canned motor. An axial zero point adjustment circuit uses a voltage supply, which varies proportionately with the power supply voltage of the canned motor, as a bias power supply to adjust the voltage difference of the axial position detection coils to zero when the rotor is at a reference position in the axial direction. Even if the power supply voltage of the canned motor varies, since the bias power supply of the axial zero point adjustment circuit varies in likewise manner, the zero point adjustment by the axial zero point adjustment circuit is not affected and axial bearing wear detection of high precision is enabled.

CROSS-REFERENCE TO PRIOR APPLICATION

This is a U.S. national phase application under 35 U.S.C. §371 ofInternational Patent Application No. PCT/JP01/11082 filed Dec. 18, 2001which is incorporated by reference herein. The International Applicationwas published in Japanese on Jun. 26, 2003 as WO 03/052904 A1 under PCTArticle 21(2).

1. Technical Field

This invention concerns an axial bearing wear detection device fordetecting bearing wear in the axial direction of a canned motor.

2. Background Art

In general, a canned motor is mainly used for driving a pump and sinceit is used in a chemical plant, etc., it is required to be high inreliability.

Since a canned motor pump has a leak-less structure in which a cannedmotor and a pump are integrated, the internal conditions cannot bemonitored visually. In many cases, the canned motor's rotor, whichrotatingly drives the pump's impeller, is supported by a slide bearingthat is lubricated by the pump fluid, and for efficient operation of thecanned motor, the wear conditions of the slide bearing must be monitoredfrom the exterior.

Thus as described for example in Japanese Examined Patent PublicationNo. 57-21924, Japanese Laid-open Patent Publication No. 10-80103, orJapanese Laid-open Patent Application No. 11-148819, an axial bearingwear detection device has been proposed with which axial positiondetection coils are disposed at both ends in the axial direction of astator of a canned motor, the axial position of a rotor, which rotateswhile being supported by a slide bearing, is detected by comparing thedifference in the voltages generated at the axial position detectioncoils, and the amount of bearing wear in the axial direction isestimated from this axial position of the rotor.

FIG. 6 is a circuit diagram of a conventional axial bearing weardetection device.

An axial bearing wear detection device 11 has axial position detectioncoils Cf and Cr, disposed at the two parts of the front side and rearside of a stator. These axial position detection coils Cf and Cr areconnected in series and an intermediate part 12 is grounded. An end part13 of axial position detection coil Cf at the front side of the statoris connected to one input side of a differential amplifier 16 via anamplifier 14 and a rectifier/smoothing circuit 15, an end part 17 ofaxial position detection coil Cr at the rear side of the stator isconnected to the other input side of a differential amplifier 16 via anamplifier 18 and a rectifier/smoothing circuit 19, and the output sideof differential amplifier 16 is connected to an output terminal 21 viaan axial zero point adjustment circuit 20.

In order to accurately detect the axial position of a rotor from thedifference of the voltages generated at the respective axial positiondetection coils Cf and Cr, the relationship between the signal of thedifference of the voltages generated at the respective axial positiondetection coils Cf and Cr and the axial position of a rotor must beadjusted, that is, zero point adjustment must be performed, and axialzero point adjustment circuit 20 is provided for this zero pointadjustment.

A variable resistor 22 is connected to axial zero point adjustmentcircuit 20, a negative voltage V− of a constant voltage power supply isconnected to one terminal 23 of variable resistor 22, and a positivevoltage V+ of the constant voltage power supply is connected to theother terminal 24 of variable resistor 22.

FIG. 7 is a graph showing the relationship between the voltagesgenerated at axial position detection coils Cf and Cr and the axialposition of the rotor.

The ordinate axis of this graph indicates the AC output voltagesgenerated at axial position detection coils Cf and Cr and the abscissaaxis indicates the axial position of the rotor, with the central 0 mmposition indicating the mechanical center position of the rotor, theleft negative side indicating the rear side of the canned motor, and theright positive side indicating the front side.

The point at which the curve of the voltage generated at axial positiondetection coil Cf and the curve of the voltage generated at axialposition detection coil Cr intersect is the electrical central positionat which the voltages generated at the respective axial positiondetection coils Cf and Cr are equal. Due to reasons of design ormanufacture, a deviation arises between the electrical central positionand the mechanical central position, and with the case shown in FIG. 7,there is a deviation of approximately 1 mm.

Thus to adjust the electrical deviation of approximately 1 mm withrespect to the mechanical 0 mm central position by means of axial zeropoint adjustment circuit 20, shown in FIG. 6, the electrical outputsignal when the rotor is at 0 mm, which is the mechanical centralposition, is adjusted to be canceled out by the positive and negativepower supply V+ and V− of the constant voltage power supply via variableresistor 22.

FIG. 8 is a graph showing how the voltages of FIG. 7, which aregenerated at axial position detection coils Cf and Cr, vary when thepower supply voltage of the canned motor varies.

For example, with respect to the voltages generated at axial positiondetection coils Cf and Cr when the power supply voltage of the cannedmotor is 200V, the voltages generated at axial position detection coilsCf and Cr increase when the power supply voltage increases, for example,to 220V, and the voltages generated at axial position detection coils Cfand Cr decrease when the power supply voltage decreases, for example, to180V. The curves of the voltages generated at the respective axialposition detection coils Cf and Cr with respect to the axial positionare shown to move substantially in parallel with a variation of thepower supply voltage.

FIG. 9 is a graph showing the output when the voltages of FIG. 7, whichare generated at axial position detection coils Cf and Cr, are processedby an axial bearing wear detection device that includes the conventionalaxial zero point adjustment circuit 20 shown in FIG. 6.

By performing zero point adjustment with axial zero point adjustmentcircuit 20 when the power supply voltage of the canned motor is 200V,the relationship between the axial position of the rotor and the outputfrom output terminal 21 becomes a substantially straight line thatpasses through 0V when the axial position is 0 mm.

However, when the power supply voltage of the canned motor differs fromthat during zero point adjustment, that is for example, when the powersupply voltage increases to 220V or decreases to 180V, the curve of theoutput with respect to the axial position moves in parallel, causing thezero position reference to change.

The variation of the difference of the axial position detection coils Cfand Cr for the 0 mm axial position according to the magnitude of thepower supply voltage is considered to be a cause of this problem. Thatis, when the power supply voltage differs from that during zero pointadjustment, since the voltages generated at the respective axialposition detection coils Cf and Cr vary as shown in FIG. 8, the voltagedifference of axial position detection coils Cf and Cr when the rotor isat the 0 mm position changes and will be in accordance with the parallelmovement of the output characteristics, such as shown in FIG. 9.

If the output characteristics with respect to axial position are asshown in FIG. 9, in a certain case where the power supply voltage of thecanned motor differs from that during zero point adjustment, the axialposition reference shifts to either the front side or the rear side sothat when the power supply voltage of the canned motor fluctuates, theinformation that the bearing is worn maybe output when the bearing isactually not worn or the information that the bearing is not worn may beoutput when the bearing is actually worn.

Thus with the conventional axial zero point adjustment circuit, though aconstant voltage is supplied via variable resistor 22 from a constantvoltage power supply, which does not vary even when the power supplyvoltage of the canned motor varies, and variable resistor 22 is adjustedso that the difference of the voltages generated at axial positiondetection coils Cf and Cr will be zero when the rotor is at thereference position in the axial direction, since the voltages generatedat axial position detection coils Cf and Cr are dependent on the powersupply voltage of the canned motor and the difference of the voltagesgenerated at axial position detection coils Cf and Cr is also dependenton the power supply voltage of the canned motor, when the power supplyvoltage of the canned motor becomes a voltage that differs from thatduring zero point adjustment, erroneous operation occurs such that evenif there is no change in the axial position of the rotor, wear of thebearing is detected even though the bearing is not worn or the wear ofthe bearing is not detected even though the bearing is worn.

This invention has been made in view of this point and an object thereofis to provide an axial bearing wear detection device for canned motorthat can perform axial bearing wear detection of high precision evenwhen the power supply voltage of the canned motor varies.

DISCLOSURE OF THE INVENTION

This invention's axial bearing wear detection device for canned motorcomprises: axial position detection coils, disposed at both ends in theaxial direction of a stator of a canned motor having the stator and arotor; an axial position detection circuit, detecting the axial positionof the rotor with respect to the stator from the difference in thevoltages generated at the axial position detection coils; and an axialzero point adjustment circuit, having a power supply source, whichvaries in proportion to the power supply voltage of the above-mentionedcanned motor, as a bias power supply and adjusting to zero the voltagedifference of the two axial position detection coils at theabove-mentioned axial position detection circuit when the rotor is at areference position in the axial direction.

With this arrangement, by means of the axial position detection circuit,the movement position in the axial direction of the rotor is detectedfrom the difference in the voltages generated at the axial positiondetection coils disposed at the respective end parts in the axialdirection of the stator. The voltage difference of the two axialposition detection coils at the position detection circuit when therotor is at a reference position in the axial direction is adjusted tozero by means of the axial zero point adjustment circuit that uses avoltage source, which varies in proportion to the power supply voltageof the canned motor, as a bias power supply. Even when the power supplyvoltage of the canned motor varies, the bias power supply of the axialzero point adjustment circuit varies in the same manner, and thus thezero point adjustment by the axial zero point adjustment circuit is notaffected and axial bearing wear detection of high precision is enabled.

Also with this invention's axial bearing wear detection device forcanned motor, the voltage generated at least at one of the axialposition detection coils is used for the bias power supply of the axialzero point adjustment circuit. By this arrangement, high precision axialbearing wear detection is enabled by a simple circuit arrangement thatdoes not use a separate power supply.

Also with this invention's axial bearing wear detection device forcanned motor, the voltage generated at one of the axial positiondetection coils is used for the positive power supply of the bias powersupply of the axial zero point adjustment circuit and the voltagegenerated at the other axial position detection coil is used for thenegative power supply of the bias power supply of the axial zero pointadjustment circuit. By this arrangement, high precision axial bearingwear detection is enabled by a simple circuit arrangement that does notuse a special power supply.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of an axial bearing wear detection devicefor canned motor that is an embodiment of this invention,

FIG. 2 is a partially cutaway front view of a canned motor pump to whichthe same axial bearing wear detection device is applied,

FIG. 3 is a perspective view of a part of the same axial bearing weardetection device at which an axial position detection coil is disposedat an end part of one tooth part of a stator,

FIG. 4 is a schematic view of the canned motor pump to which the sameaxial bearing wear detection device is applied,

FIG. 5 is a graph showing the output when voltages generated at theaxial position detection coils are processed by the axial bearing weardetection device,

FIG. 6 is a circuit diagram of a conventional axial bearing weardetection device,

FIG. 7 is a graph showing the relationship between the voltagesgenerated at the axial position detection coils of the prior art and theaxial position of a rotor,

FIG. 8 is a graph showing how the voltages of FIG. 7, which aregenerated at the axial position detection coils, vary when the powersupply voltage of a canned motor varies,

FIG. 9 is a graph showing the output when the voltages of FIG. 7, whichare generated at the axial position detection coils, are processed by anaxial bearing wear detection device, which includes the conventionalaxial zero point adjustment circuit shown in FIG. 6.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of this invention shall now be described with reference toFIG. 1 through FIG. 5.

FIG. 2 is a partially cutaway front view of a canned motor pump to whichan axial bearing wear detection device is applied. 31 is a canned motorpump, and with this canned motor pump 31, a pump 32 and a radial gaptype canned motor 33 are joined integrally to each other in afluid-tight manner.

In canned motor 33, a stator 37, arranged by winding stator winding 36in stator grooves 35 of a stator iron core 34, is fitted inside a statorframe 38, a stator can 39, formed to a thin cylindrical shape fromstainless steel or other non-magnetic material, is inserted in closecontact to the inner peripheral surface of stator 37, and the respectiveend rims of stator can 39 are welded in a fluid-tight manner to statorframe 38. Also, a rotor shaft 44 is fitted into a rotor 43, arranged byattaching a rotor conductor 42 in rotor grooves 41 of a rotor iron core40, and a rotor can 45, formed to a thin cylindrical shape fromstainless steel or other non-magnetic material, is fitted onto the outerperipheral surface of rotor 43. Stator 37 and rotor 43 are disposed soas to oppose each across a can gap 46 between stator can 39 and rotorcan 45, and rotor shaft 44 is axially supported by bearings 48 a and 48b, which are slide bearings attached to bearing boxes 47 a and 47 b, andvia sleeves 49 a and 49 b and thrust collars 50 a and 50 b.

On stator iron core 34 are disposed a pair of radial position detectioncoils C1 and C2, which are spaced apart by a spatial angle of 180degrees with respect to the center of stator iron core 34 and each ofwhich is wound around the entirety of one tooth part of stator iron core34.

Canned motor 33 has a terminal box 53, which is in communication withthe interior of stator frame 38, protruding from a part of stator frame38, and at the upper part of this terminal box 53 is installed a sealedcontainer 55 with an explosion-proof structure provided with a glasspeephole. A part of an axial bearing wear detection device, which isincluded among the operation monitoring devices of canned motor 33, ishoused inside this sealed container 55.

Pump 32 has a casing 57, which is mounted in a fluid-tight manner tostator frame 38 of canned motor 33, and an impeller 58, mounted torotation shaft 44 inside casing 57. Impeller 58 inside pump 32 isrotatingly driven by rotor 43, which is supported by bearings 48 a and48 b and via sleeves 49 a and 49 b, and is restricted in movement in theaxial direction by the contact of thrust collars 50 a and 50 b withbearings 48 a and 48 b.

FIG. 3 is a perspective view of a part at which at which an axialposition detection coil of the axial bearing wear detection device isdisposed at an end part of one tooth part of the stator.

A notch groove 61 b is provided near one end part 61 a of a tooth part60 of stator iron core 34 to form a small core part 61 and one axialposition detection coil Cf is wound inside stator grooves 35 around thiscore part 61. Though not illustrated, the other axial position detectioncoil Cr is provided in likewise manner at the other end of tooth part60.

FIG. 4 is a schematic view of canned motor pump 31 to which the axialbearing wear detection device is applied. At the respective ends in theaxial direction of the upper side of stator iron core 34 of canned motor33 are installed the pair of axial position detection coils Cf and Crfor detecting the axial position of rotor 43, that is, the axial wear ofbearings 48 a and 48 b. Also, radial position detection coil C1, fordetecting the radial wear of bearings 48 a and 48 b, is installed at onetooth part at the lower side, and though not illustrated, another radialposition detection coil C2 is disposed at one tooth part that opposesradial position detection coil C1 and these radial position detectioncoils are connected in series.

Here, the detection of the axial wear of bearings 48 a and 48 b shall bedescribed. The pump 32 side of canned motor 33 shall be referred to asthe “front side” and the side opposite pump 32 shall be referred to asthe “rear side.”

With regard to the movement of rotor 43 in the axial direction, movementtowards the front side is restricted by the contacting of bearing 48 a,at the front side at which impeller 58 is positioned, with thrust collar50 a, and opposite movement towards the rear side is restricted by thecontacting of bearing 48 b with thrust collar 50 b.

Though the range in which rotor 43 can move freely in the axialdirection in the state in which there is no axial wear of bearings 48 aand 48 b, that is, the play of rotor 43 differs according to the sizeand arrangement of pump 32, it is approximately 1 to 2 mm, and in normaloperation, rotor 43 is positioned within this range of play in the axialdirection.

Though in normal operation, the axial position of rotor 43 is at aposition at which front side bearing 48 a and thrust collar 50 a rotatewhile in contact with each other or a position at which rear sidebearing 48 b and thrust collar 50 b rotate while in contact with eachother, the structure is such that when bearings 48 a and 48 b becomeworn by approximately 1 mm in the axial direction, the front surface orthe rear surface of impeller 58 of pump 32 contacts casing 57 or bearingbox 47 a.

Thus in consideration of the above, for detection of the axial wear ofbearings 48 a and 48 b, the movement of rotor 43 in the axial directionmust be monitored within a range of ±2.5 mm.

And upon installing axial position detection coils Cf and Cr at therespective end parts of stator iron core 34, the axial movement of rotor43 can be made known from the difference in the voltages generated atthese axial position detection coils Cf and Cr.

FIG. 1 shows a circuit diagram of the axial bearing wear detectiondevice.

71 is an axial wear detection part. This axial wear detection part 71has axial position detection coils Cf and Cr, disposed at the respectiveend parts of stator 37, and these axial position detection coils Cf andCr are connected in series, with intermediate part 72 being grounded.

An end part 73 of axial position detection coil Cf at the front side ofstator 37 is connected via an amplifier 74 to a rectifier/smoothingcircuit 75, which converts the voltage of the coil to a positive DCvoltage. An end part 76 of axial position detection coil Cr at the rearside of stator 37 is connected via an amplifier 78 to arectifier/smoothing circuit 79, which converts the voltage of the coilto a negative DC voltage. These rectifier/smoothing circuits 75 and 79are connected to input parts of an adding amplifier circuit 80.

The voltage generated at axial position detection coils Cf and Cr areconverted into positive and negative DC voltages respectively and theninput into adding amplifier circuit 80. Adding amplifier circuit 80synthesizes these DC voltages and outputs a voltage proportional to thesynthesis result to output terminal 81. To output terminal 81 isconnected a display device, etc., which displays the degree of axialwear corresponding to the movement direction and movement position ofrotor 43 in accordance with the voltage output from adding amplifiercircuit 80.

Axial position detection circuit 82 for detecting the axial position ofrotor 43 relative to stator 37 from the difference in the voltagesgenerated at axial position detection coils Cf and Cr comprisesamplifiers 74 and 78, rectifier/smoothing circuits 75 and 79, addingamplifier circuit 80, etc.

To adding amplifier circuit 80 is connected an axial zero pointadjustment circuit 83, which uses a voltage supply that varies inproportion to the power supply voltage of canned motor 33 as a biaspower supply and adjusts to zero the voltage difference of axialposition detection coils Cf and Cr at axial position detection circuit82 when rotor 43 is at an axial direction reference position. This axialzero point adjustment circuit 83 has a variable resistor 84 for zeropoint adjustment, one end part 85 of this variable resistor 84 isconnected to the positive output of axial position detection coil Cf atone side, another end part 86 is connected to the negative output ofaxial position detection coil Cr at the other side, and an intermediatepoint is connected to the input of adding amplifier circuit 80.

At adding amplifier circuit 80 of axial position detection circuit 82, avoltage corresponding to the axial movement of rotor 43 is output basedon the difference in the voltages generated at axial position detectioncoils Cf and Cr that are disposed at the respective ends in the axialdirection of stator 37.

At axial zero point adjustment circuit 83, the voltage difference ofaxial position detection coils Cf and Cr at adding amplifier circuit 80when rotor 43 is at the axial direction reference position is adjustedto zero, using the voltage supply that varies in proportion to the powersupply voltage of canned motor 33 as the bias power supply. That is,zero point adjustment is performed by means of variable resistor 84 sothat the voltage output to output terminal 81 will be 0V when rotor 43is at 0 mm, which is the mechanical center position.

FIG. 5 is a graph showing the output when voltages generated at axialposition detection coils Cf and Cr are processed by the axial bearingwear detection device.

The abscissa axis of the graph indicates the axial position of rotor 43and the ordinate axis indicates the voltage that is output to outputterminal 81 of adding amplifying circuit 80.

Since the power supply of axial zero point adjustment circuit 83 is nota constant voltage power supply and the voltages generated at axialposition detection coils Cf and Cr are converted to positive andnegative DC voltages respectively and then used as voltages for zeropoint adjustment, when the power supply voltage of canned motor 33varies and the difference voltage of axial position detection coils Cfand Cr vary, the voltage for zero point adjustment varies in likewisemanner. Thus even if the power supply voltage of canned motor 33 varies,the function of zero point adjustment by axial zero point adjustmentcircuit 83 is not obstructed.

In the graph of FIG. 5, the outputs of adding amplifier circuit 80 areshown with the power supply voltage of canned motor 33 as a parameter,that is, the outputs for a power supply voltage of 180V, 200V, and 220Vare shown. However, it was confirmed that there was hardly any deviationof the output for the 0 mm axial position.

The three curves shown in the graph do not coincide but deviate withrespect to each other slightly because the magnitudes of the outputvoltages of the respective axial position detection coils Cf and Cr withrespect to axial position vary according to the power supply voltage ofcanned motor 33, that is, when the power supply voltage of canned motor33 increases, the slope of the curve decreases, and when the powersupply voltage of canned motor 33 decreases, the slope of the curveincreases. Deviations of such a level are within a tolerable range.

Thus in comparison to the case of the prior-art axial zero pointadjustment circuit shown in FIG. 9, the influence of the variation ofthe power supply voltage of canned motor 33 is not received and axialbearing wear detection of high precision is enabled.

Since by means of axial zero point adjustment circuit 83, the voltagedifference of axial position detection coils Cf and Cr at axial positiondetection circuit 82 when rotor 43 is at the axial direction referenceposition is adjusted to zero using a voltage supply that varies inproportion to the power supply voltage of canned motor 33 as the biaspower supply as described above, even if the power supply voltage ofcanned motor 33 varies, the bias power supply of axial zero pointadjustment circuit 83 varies in likewise manner such that the zero pointadjustment by axial zero point adjustment circuit 83 is not affected andaxial bearing wear detection of high precision is enabled.

Moreover, by using the voltage that is generated at one axial positiondetection coil Cf for the positive power supply of the bias power supplyof axial zero point adjustment circuit 83 and using the voltage that isgenerated at the other axial position detection coil Cr for the negativepower supply of the bias power supply of axial zero point adjustmentcircuit 83, axial bearing wear detection of high precision is enabledwith a simple circuit arrangement that does not use a separate powersupply.

At least one of the voltages generated at axial position detection coilsCf and Cr may be used for the power supply of axial zero pointadjustment circuit 83, and even in this case, axial bearing weardetection of high precision is enabled with a simple circuit arrangementthat does not use a separate power supply.

Also, the bias power supply of axial zero point adjustment circuit 83 isnot restricted to the use of voltages generated at axial positiondetection coils Cf and Cr and another power supply that varies involtage in conjunction with the power supply voltage of canned motor 33may be used instead, and axial bearing wear detection of high precisionis enabled in this case as well.

INDUSTRIAL APPLICABILITY

This invention's axial bearing wear detection device for canned motorenables axial bearing wear detection of high precision and in additionto application to canned motor pumps used in chemical plants, etc., thisinvention may be applied to various equipment that use canned motors.

1. An axial bearing wear detection device for canned motor comprising:axial position detection coils, disposed at both ends in the axialdirection of a stator of a canned motor having the stator and a rotor;an axial position detection circuit, detecting the axial position of therotor with respect to the stator from the difference in the voltagesgenerated at the axial position detection coils; and an axial zero pointadjustment circuit, having a power supply source, which varies inproportion to the power supply voltage of said canned motor, as a biaspower supply and adjusting to zero the voltage difference of the twoaxial position detection coils at said axial position detection circuitwhen the rotor is at a reference position in the axial direction.
 2. Theaxial bearing wear detection device according to claim 1, wherein thevoltage generated at least at one of the axial position detection coilsis used for the bias power supply of the axial zero point adjustmentcircuit.
 3. The axial bearing wear detection device according to claim1, wherein the voltage generated at one of the axial position detectioncoils is used for the positive power supply of the bias power supply ofthe axial zero point adjustment circuit and the voltage generated at theother axial position detection coil is used for the negative powersupply of the bias power supply of the axial zero point adjustmentcircuit.